Membrane technology has become a highly efficient separation technology for industrial applications over the past few decades. The key requirements for porous ceramic membranes are mechanical stability, controlled pore morphology, and high permeability. However, only a few studies have been conducted to optimise commercial membrane filters. In this study, a multichannel cylindrical-tube-type support with a microfiltration (MF) coating was prepared. To design a reliable porous structure and avoid shrinkage defects, the support layer was extruded using a combination of different-sized Al₂O₃ particles. The alumina microfiltration coating was developed using multiple dip-coatings to control the membrane thickness. An inorganic surface modification was conducted for the first time on an extruded membrane using a SiO₂ sol-gel technique to enhance the antifouling properties. Furthermore, the membrane properties were investigated with scanning electron microscopy, mercury porosimetry, and a dead-end microfiltration system.

We introduced a modified sol-gel method using polyvinyl alcohol (PVA) as an additive to improve the permeability of γ-Al₂O₃ membranes by minimizing the thickness of the selective layer and maximizing the porosity. First, the analysis revealed that the thickness of γ-Al₂O₃ decreased as the concentration of PVA increased in the boehmite sol. Second, the properties of the γ-Al₂O₃ mesoporous membranes were greatly influenced by the modified route (method B) compared to the conventional route (method A). The results showed that the porosity and surface area of the γ-Al₂O₃ membrane increased, and the tortuosity decreased considerably using method B. This effect was attributed to the adsorption of PVA molecules on the surface of the boehmite particles, which depended on the synthesis route. The experimentally determined pure water permeability trend and the Hagen–Poiseuille mathematical model confirmed that the modified method improved the performance of the γ-Al₂O₃ membrane. Finally, the γ-Al₂O₃ membrane fabricated via a modified sol-gel method with a pore size of 2.7 nm (MWCO = 5300 Da) exhibited a pure water permeability of over 18 LMH/bar, which is three times higher than that of the γ-Al₂O₃ membrane prepared using the conventional method.

Compared to traditional membrane materials, alumina membranes are particularly beneficial for industrial wastewater treatment. However, the development of mesoporous α-alumina membranes for ultrafiltration applications is still a challenge due to uncontrolled pore size. In this study, we optimized the sol-gel method for the fabrication of a high-performance mesoporous α-alumina membrane. The peptization conditions (pH and peptization time) and phase transformation of boehmite were investigated to achieve better properties of the α-alumina membrane. The surface properties of the membrane were observed to be improved by reducing the system pH to 3.5 and increasing the peptization time to 24 h. The effect of sintering temperature on the phase transformation behavior, microstructures and performance of the membranes was also elucidated. An α-alumina ultrafiltration membrane with an average thickness of 2 μm was obtained after sintering at 1100 °C. The molecular weight cut-off of the α-alumina membrane, as obtained by the filtration of aqueous PEG solution, was approximately 163 kDa (12.5 nm). This is the smallest pore size ever reported for pure α-alumina membranes.